The present invention relates to the chemical sterilization process for articles such as contact lenses. More particularly, this invention concerns an improved method of chemical sterilization and apparatus adapted to be employed with said improved method, or with other types of similar chemical processes wherein a chemical reaction is to be delayed for a specified period of time.
The present invention evolved with regard to sterilization techniques for contact lenses, and will be described with reference to this specific use. It should be kept in mind, however, that this is done for purposes of description, and not by way of limitation.
For many years, corneal contact lenses constructed of relatively hard plastics have been in use. These lenses, while effective, have a disadvantage in that they often produce discomfort to the wearer, and thus in many instances can only be worn for short durations. Recently, there has been developed an extremely soft contact lens which fabricated from a pliable plastic material is thus less likely to cause discomfort. These pliable plastics are quite hydrophlic, and accordingly are susceptible to contamination by microorganisms. As such, the user of these newer, softer lenses must take care to sterilize his, or her lenses daily.
A number of sterilizing techniques have been developed, several of which utilize the heating of the lenses in a closed vessel, in the presence of a saline solution, heating taking place to a sufficiently high temperature to achieve destruction of contaminants, such as micro-organisms. There has also been proposed, more recently, a sterilizing process which does not utilize heating, but rather employs an anti-microbial solution, such as for example hydrogen peroxide (H.sub.2 O.sub.2).
With the previously employed techniques utilizing heating, the only concern regarding safety to the wearer, was that the lenses and capsule cool sufficiently. Where an anti-microbial sterilizing agent is used, care must be taken to insure that the solution is in someway neutralized prior to insertion of the lens into the eye. If this is not done, there is a distinct danger of damage to the eye, and at the very least discomfort to the user.
There has been proposed a process of sterilization wherein hydrogen peroxide is employed as the anti-microbial agent, in a relatively weak concentration, on the order of a 3% solution. As to subsequent decomposition, the sterilizing solution provides a reactant which when brought into contact with a catalytic agent, such as platinum, will produce a chemical reaction resulting in neutralization or decay of the hydrogen peroxide. In this regard, oxygen is liberated and the hydrogen peroxide is reduced to water. The whole process takes place over a period of time, depending of course on the nature of the catalytic agent and the strength of the original solution, but the end result is a sufficiently decayed solution which will permit the lenses to be removed and disposed on the wearer's corena without danger of discomfort or damage.
Even with the above-discussed process, there are certain safety considerations. In this regard, the initial concentration of the sterilizing solution must be quite low, on the order of three percent (3%). This low concentration is employed as a safety factor in that should the user accidently insert the lenses, prior to decomposition of the hydrogen peroxide, only discomfort will result, rather than serious damage. A problem does exist, however, in that in order to achieve the desired degree of sterilization, the contact lenses must be subjected to a solution of adequate strength for a sufficient duration. With the above-discussed process, where a catalytic agent is used to produce a decaying chemical reaction, a reduction in strength of the hydrogen peroxide commences immediately, with the solution decaying rapidly. The overall decaying process, as a function of time and strength of solution, is indicated generally in the dotted portion of the graph of FIG. 9 of the drawings. As such, since it is not practical to employ strong solutions, and further since decay of the hydrogen peroxide will start as soon as it is brought into contact with a catalyst, there is a distinct possibility that insufficient sterilization may result.